engine: Log when gluster task started from CLI

Add event log messages when a gluster task - rebalance
or remove brick - is started from CLI

Change-Id: I381ecc028ff5dd36202916953f5c3c623b43e526
Bug-Url: https://bugzilla.redhat.com/1015444
Signed-off-by: Sahina Bose <sabose@redhat.com>